In recent years, topological PCS waveguides
have been demonstrated
[1]}, [2]}, which may suppress disorder-induced
backscattering through “topological protection.”
Moreover, PCS waveguides also exhibit Bloch modes with local chirality [3]}, [4]}, [5]},
which can be used to couple to spin charged quantum dots, manifesting in unidirectional single photon emission.
Unfortunately, many of the topological PCS waveguide modes fall above the light line and are thus intrinsically lossy, with significant propagation losses [6]}.
Very recently, new classes of topological PCS waveguides have been presented,
using the so-called Valley Hall effect
[7]}, [8]},
which more easily
allow edge state modes to fall below the light line.
For future applications of these topological PCS structures, one goal is to increase the operation bandwidth for single mode operation below the light line.
